The nurse shark's scientific name, Ginglymostoma cirratum, derives from Greek and Latin origins. "Ginglymostoma" translates to "hinged mouth" in Greek, referring to the unique structure of the shark's mouth. Meanwhile, "cirratum" means "having curled ringlets" in Latin, alluding to certain physical features of the species. The nurse shark is believed to be closely related to other sharks, such as Nebrius, Pseudoginglymostoma brevicaudatum, Rhincodon typus, and Stegostoma fasciatum, forming a clade within the elasmobranch family.
The nurse shark possesses distinctive characteristics, including two rounded dorsal fins, rounded pectoral fins, an elongated caudal fin, and a broad head. While there have been reports of larger nurse sharks, the maximum documented length stands at 3.08 meters (10 ft 1+1⁄2 in), with weights up to 330 kilograms (730 lb). Adult nurse sharks typically exhibit a brownish coloration, while newborns display a spotted pattern that fades over time. As they develop, these sharks reach a length of approximately 30 centimeters.
Nurse sharks have a wide but patchy geographical distribution, inhabiting tropical and subtropical coastal waters. In the Eastern Atlantic, their range extends from Cape Verde to Gabon, with occasional sightings as far north as France. Along the Western Atlantic and the Caribbean, nurse sharks can be found from Rhode Island to southern Brazil. In the East Pacific, their habitat spans from Baja California to Peru.
These sharks prefer inshore environments, with juveniles often residing in shallow coral reefs, seagrass flats, and around mangrove islands. Adult nurse sharks, on the other hand, tend to dwell in deeper reefs and rocky areas, seeking shelter in crevices and under ledges during the day. At night, they venture out to feed on the seabed in shallower regions.
As opportunistic predators, nurse sharks primarily feed on small fish like stingrays and various invertebrates such as crustaceans, mollusks, and tunicates. They exhibit nocturnal behavior, foraging through bottom sediments during the night. Although nurse sharks have relatively small mouths, they possess powerful suction forces, allowing them to consume prey items of considerable size. In some cases, they employ a suck-and-spit behavior or shake their heads vigorously to reduce the size of their food.
Compared to other shark species, nurse sharks are exceptionally sedentary. They display strong site fidelity, often returning to the same breeding grounds repeatedly. Additionally, nurse sharks form large sedentary groups during the day, creating an interesting social dynamic. However, despite their seemingly calm nature, nurse sharks rank fourth in documented shark bites on humans. This can be attributed to incautious behavior by divers who misjudge the shark's temperament.
Nurse sharks are ovoviviparous, with the female retaining the fertilized eggs inside her body until they hatch. The mating cycle of nurse sharks occurs every two years, with females requiring up to 18 months to produce a new batch of eggs. The mating season typically spans from late June to the end of July, and the gestation period lasts for six months. A female nurse shark typically gives birth to a litter of 21–29 fully developed pups measuring approximately 30 centimeters in length.
Research has shown that nurse sharks engage in multiple paternity during the mating season, resulting in increased genetic variation within broods. A study spanning ten years found that a brood of nurse sharks exhibited more genotypes than those with a single father. This behavior promotes genetic diversity within the species and contributes to its overall resilience.
Coastal habitats shared by nurse sharks and American alligators (Alligator mississippiensis) or American crocodiles occasionally lead to encounters between these species. Historical accounts and photographic evidence suggest that predation events involving nurse sharks do occur. Such interactions highlight the complex dynamics within these marine ecosystems and the interdependencies between different species.
The nurse shark plays a crucial role in shark research due to its robust nature and ability to tolerate capture, handling, and tagging. While the nurse shark is considered a species of least concern in the United States and The Bahamas, it is globally assessed as Vulnerable by the IUCN List of Threatened Species. The vulnerable status in South America, Central America, and the Caribbean reflects the reported threats faced by nurse sharks in those regions.